Hydrogen permeation through nickel and nickel alloys: surface reactions and trapping.
The Open University.
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The frequency variations of attenuation and phase lag of the modulated gas flow through thin metal foils have characteristic features whether permeation is diffusion controlled, is influenced by surface reactions or affected by interna1 trapping.
Analysis of data obtained for hydrogen permeation through nickel show that hydrogen is dissociatively chemisorbed in nickel.
The permeation parameters diffusivity, permeability and surface reaction rate obtained for nickel are:
D/(m2s-1) = 7.12 x 1-7 exp [-4.64 x 103/RT/(K)]
Pm/(molH2m-1s-1Pa-1/2 = 3.35 x 10-7 exp[-54.25 x 103/RT/(K)]
Ksm/(molH2m-3Pa-1/2) = 0.47 exp[-13.6 x 103/RT/(K)]
K1/(molH2m-2s-1Pa-1) = 1.44 x 1-6 exp[-29.68 x 103/RT/(K)]
The experiments conducted on cold-worked nickel have revealed that hydrogen is trapped within the bulk during the permeation in this material.
A series of experiments conducted on cold worked nickel+2% thoria has also revealed that hydrogen is trapped within the bulk during the permeation. Analysis of data obtained for cold worked nickel+2% thoria suggest that hydrogen is trapped at the dislocation networks around thoria particles.
Frequency variation of attenuation and phase lag of the modulated flow show that hydrogen trapping in both cold-worked nickel and nickel+2% thoria is in dynamic equilibrium. A trap depth of 40 kJ/mol has been obtained for nickel+2% thoria.
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